1. Field of Invention
This invention relates to redundant multi-stage switching networks, specifically to the non-stop addition of a new row to such a network.
2. Discussion of Prior Art
When a multi-stage switching network such as a Banyan or Butterfly network is expanded a new row must be added. Adding a new row requires that half of the external connections have to be disconnected in the process. This leads to an interruption in service.
A Butterfly network, 10, is shown in FIG. 1 with top ports, 11, connected to external connections, 12, and bottom ports, 13, connected to external connections, 14. A duplicate of this network, 15, with top ports, 16, and bottom ports, 17. A new row, 18, with top ports, 19, and bottom ports, 20, are also shown.
In order to double number of external connections of the Banyan network, 10, the connections between the top ports, 11, and external connections, 12, have to be broken and connected to the left half of new row bottom ports, 20, and the external connections, 12, connected to the left half of new row top ports, 19. To complete the upgrade, the duplicate network top ports, 16, are connected to the right half of new row bottom ports 20. At this point, duplicate network bottom ports, 17, and right half of new row top ports 19 would be available for new external connections.
The problem is that the connections between the original network top ports 11, and external connections, 12, have to be disconnected in the process. This leads to an interruption in service.
Currently, special “hot slide” multiplexers are designed into switching centers to allow a new switching network to be installed in parallel and then switched in between clock cycles. Unfortunately, this physical electrical switch-over is only part of the problem. The new switch has to have exactly the same “control state” information as the old switch. This requires a considerable amount of hardware and software to accomplish correctly.
Objects and Advantages
Accordingly, the several objects and advantages of my invention are:                (a) to provide a procedure by which a redundant multi-stage switching network can be upgraded without having to break an external connection; and        (b) to provide a procedure by which a redundant multi-stage switching network can be upgraded with a minimum loss in throughput bandwidth.        
Further objects and advantages of our invention will become apparent from a consideration of the drawings and ensuing description.